Power tools may be of different types depending on the type of output provided by the power tool. For example, a power tool may be a drill, hammer, grinder, impact wrench, circular saw, reciprocating saw, and so on. Some power tools may be powered by an alternating current (AC) power source or a direct current (DC) power source such as a battery pack. In power tools using a brushless DC (BLDC) motor, a series of electronic switches are used to electronically energize motor windings sequentially in order to drive the motor rotor. Using these switches, the speed and rotational direction of the rotor can be controlled.
In power tools having brushless DC motors powered by an Alternating Current (AC) power source, a rectifier circuit is often employed to convert negative portions of the current waveform to positive current needed to drive the motor. Using motor control schemes conventionally used with DC power sources, which have a nearly-linear voltage waveform, encounters challenges when used on power tools powered by AC power sources. These challenges relate to the non-linear voltage waveform of the AC power supply and to certain inherent electrical characteristics of the motor that affect current draw from the power supply, which contribute to reduced power factor and motor efficiency. What is needed is a motor control scheme that addresses these challenges.